Impacts Of Climate Change On Typical Ecohydrological Variables In The Upper-Middle Reaches Of Heihe River Basin

The Heihe River Basin is a typical cold and arid inland river basin in China,and also one of the sensitive areas to climate change.However,few studies have been made on the impacts of climate change on ecohydrological processes in the basin so far.Models,as most effective ways to explore the ecohydrological processes,have been widely used in the related studies by many scholars.In this paper,the LPJ-GUESS model is modified and adjusted to be suitable for Heihe River Basin.The input gridded climate datasets of mean monthly temperature,precipitation,sunshine percentage and mean yearly concentration of CO₂ for the study area（the upper and middle reaches of Heihe River Basin）from 1979–2010 at 0.1°spatial resolution（≈10km）are used to run the modified LPJ-GUESS model.The output of the model includes such ecohydroligical variables as vegetation distributions,LAI（Leaf Area Index）and NPP（Net Primary Product）.RCP4.5 and RCP8.5,the two future climate scenarios produced by the FGOALS_g2 land surface model,are then used to drive the modified LPJ-GUESS model to simulate ecohydrological processes for the period of 2011-2100,for the purpose of analyzing the response of ecosystem to climate change over the study area in the future.Main conclusions obtained from this study are as follows:（1）The LPJ-GUESS model is modified in PFTs（Plants functional types）parameters,and finally proved to be applicable to Heihe River Basin with debugging for many times.The simulation results are comparable with the data from many different sources.From the perspective of vegetation,the model can accurately simulate the vegetation types in the study area,and the simulation of vegetation distribution pattern for the upper reach shows better than that for the middle reach.From LAI,the simulated values keep close to those from the remote sensing retrieval,and the deterministic coefficient reaches 0.78（p<0.01）,MAE is 0.43,and MRE is 36%;the errors in winter LAI show the largest,which is possibly related with the low vegetation coverage in this season.From NPP,the simulation for the upper reach is better than that for the middle reach,and the overall simulation results present slightly larger than those from the previous researches.As a whole,the modified LPJ-GUESS model has a good applicability in Heihe River Basin.（2）During the historical period of 1979-2010,the interannual LAI shows increasing trend overall and its multi-annual mean amounts to 8.39.The innerannul LAI changes significantly,keeping consistent with the changes of temperature and precipitation.However,the response of both inerterannal and innerannual LAI to precipitation and temperature are lagging behind.The multi-annual mean NPP in the study area is 10.47 Tg·a^-1,and the annual mean NPP is135.6 g·m^-2·a^-1.And the trends of annual NPP are consistent with the changes of temperature and precipitation,without the phenomenon of hysteresis.The NPP of PFTs are characterized by relatively obvious rising trends,except for the two Herb types.（3）Under the climate change conditions for the future period of 2011-2100,annual mean temperature and precipitation will significantly increase based on the scenarios of RCP4.5 and RCP8.5,and the increments from RCP8.5 scenario will be greater than those from RCP4.5.From the perspective of vegetation,the distribution patterns and compositions from the two scenarios in the study area will change significantly,while no variations are found in PFTs.From LAI,the LAI of the study area will keep on rise in the future.In RCP4.5 scenario,study area ecosystem will become stable till 2070s;while in RCP8.5 scenario,the vegetation will continue to grow and expand.From NPP,compared with the historial period,all the vegetation types of NPP will increase,although the trends and extents of increasing are a little different from both scenarios.Furthermore,after the half past of 21st century,the NPP for all the frigid zone vegetation types will decrease with different degrees,including the BBS and CoH,except for BNE which has strong ability in adapting the environment.